Different techniques have been developed for transporting information over a network, such as packet switching techniques whereby digitized data is arranged into so-called bit packets, and circuit switching techniques. In packet switching, the bit packets may either be of fixed length like in the Asynchronous Transfer Mode (ATM) where the packets, also called cells, are all of a conventional fixed length, or be of variable length.
ATM has been recognized as the common base on which different types of services and networks can operate. The ATM technology can efficiently combine the transmission of speech, video, audio (what is commonly called the multimedia traffic) and computer data into the wired network. Furthermore, ATM has proven to scale well from very high speed network infrastructure (the information highways) to customer premises networks. One of the great advantages of the ATM technology is the fact that it can guarantee some level of service when an ATM connection is set up. Such guarantees can correspond to transmission rate, transmission latency and information loss. They can be achieved mainly because the ATM architecture assumes that the transmission media are almost error free.
At the beginning of the ATM technology, there were only Permanent Virtual Connections (PVC). Switched Virtual Connection (SVC) were soon developed. SVCs supported the growth of ATM by providing bandwidth on demand, in real time, to any user destination, with custom-tailored performance to meet the needs of almost any application. From the beginning, SVCs have been integrated to ATM specifications and most ATM customer equipment supports SVCs.
To establish a SVC connection, a routing procedure takes place during which the control point of the source node determines the best route to the destination node. Afterwards, the source control point sends a call setup message, a copy of which is delivered to the control point of every switching node on the route. The call setup message includes all the critical information needed to define and support a connection, and is based upon information contained in the request initiated by an end user or an application. When routing the connection, the network ensures that the selected path has sufficient resources to support the traffic descriptor, bearer capability and Quality of Service (QoS) parameters specified in the call setup message. This is done by the Connection Admission Control (CAC). Then, when the call setup message is received at the destination node, a confirmation message is sent back to the source node which can initiate the exchange of information between the source node and the destination node.
All these procedures for establishing a connection are controlled by the control plane managed by a control point in each node of the network.
ATM networks are getting more and more complex and are being used to handle critical data. Therefore, the control plane is more and more complex and becomes a critical element of such networks. Unfortunately, there is currently no tool to test and verify that the control plane of a network (formed of the control planes of network nodes used in the connection) works properly in a real environment (e.g. a production network).
A solution known as Internet Protocol (IP) “Ping”, was been originally designed to check the availability of a path in the IP world and whether a destination device could be reached by sending out an echo ICMP (Internet Control Message Protocol) to the specified destination device and just waiting for an acknowledgment sent back by the destination device. This procedure is mainly used for networks of routers. Even if a “Ping” works, this cannot ensure that a data stream will actually flow because of the connectionless nature of IP. There is no control plane insofar as the path is determined at the time when the data is sent in the network. Furthermore, there are no Quality of Service parameters.
One advantage of the ATM is its ability to integrate the IP protocol. For that, the first step is to define Higher Layer Protocols (HLP) to emulate the LAN protocols above ATM. Thus, LAN emulation and classical IP are widely used. The advantage is that the applications developed on top of an IP stack are still working transparently. Of course, the “Ping” function is still implemented when IP is used on top of these HLPs since, due to the connection-oriented nature of ATM, the connection must be established prior to the data transmission.
The problem with the HLPs is that they require an extra process to actually establish a connection between two users. In fact, an additional server is necessary to translate the addresses of HLPs (e.g. IP addresses) into ATM and vice-versa. That is why each user must first register to the server before doing anything else and in particular trying to do a “Ping”. This is not very satisfying for testing the connectivity because the “Ping” procedure may not work for reasons which are unrelated to the control plane such as when the server has failed. Therefore, the HLPs do not integrate the full QoS capabilities of ATM.
Another solution for checking if an ATM connection is working properly is to use Operation Administration Management (OAM) cells. OAM cells were designed to test an ATM network through the user plane. Unfortunately, OAM cells do not trigger the control plane and in particular the Connection Admission Control (CAC). Besides, a connection must be established prior to the use of OAM cells. In fact, OAM cells simply check the physical path but do not test the establishment of a connection characterized by specific traffic parameters.